The present invention generally relates to a storage system and more particularly, to a controlled atmosphere storage system which is utilized in the field of storing perishable foodstuffs such as fruit, vegetables, etc. as a storing system for suppressing breathing action or respiration, and activities of microbes, enzyme, etc. through adjustments of composition of air in the atmosphere in which the perishables are placed.
Conventionally, the controlled atmosphere storage system (referred to as CA storage system hereinafter) as described above is so arranged that fuel fed from a container such as a cylinder or the like is mixed with air supplied from a refrigerator by a circulating blower so as to be burnt in a carbon dioxide generator for generation of carbon dioxide. Since the carbon dioxide generated in the carbon dioxide generator is supplied into the refrigerator, oxygen in the refrigerator is reduced, while carbon dioxide therein is increased. When the concentration of the carbon dioxide reaches a preset value, a scrubber is operated for adsorption of excessive carbon dioxide. Subsequently, upon arrival of the oxygen concentration at the preset value, the carbon dioxide generator is stopped, and an oxygen replenishing blower is operated so as to maintain constant, the composition of air in the atmosphere (referred to as CA gas hereinafter) in which perishable stuffs are placed for storing such perishables under a fresh state.
The known CA storage system as referred to above, however, has such a disadvantage that when a gas fuel of a petroleum group is employed as a fuel therefor, a large amount of water vapor is contained in an exhaust gas, and thus, a very large condenser is required for condensation of such water vapor, undesirably resulting in a large size of the storage system on the whole.
The problem related to the generation of water vapor may be avoided if a solid fuel having a high purity in carbon content is employed for the fuel. However, as compared with the gas fuel of petroleum group, it is difficult for the carbon fuel to maintain proper combustion, unless the temperature of a burning section is kept at a high level. Moreover, as the combustion proceeds, concentration of oxygen within the refrigerator is lowered, with a consequent reduction of the amount of oxygen to be used for the combustion, and therefore, the amount of air to be fed to the carbon fuel must be increased in order to maintain the fuel consumption, and it becomes difficult to maintain the burning section at high temperatures. In other words, it becomes impossible to keep the temperature at which the carbon fuel can maintain the combustion, unless heat recovery and heat insulation at the burning section are improved. However, if it is intended to maintain the temperature by winding the insulating material in many layers, there may be invited such problems that, not only the weight of the system is increased due to the increase in the amount of insulating material used, but also a long time is required for the preheating before ignition and stabilization of the combustion owing to an increase in the heat capacity.
Additionally, in the case where re-ignition is to be effected from a state in which the oxygen concentration in the refrigerator is low, if it is intended to carry out the combustion at the similar combustion rate to that when the oxygen concentration is normal, the circulating air amount immediately after the starting of burning becomes very large. Accordingly, there also arises such a problem that, even when the carbon fuel is particularly heated up to a temperature capable of burning, it is undesirably cooled by the circulating air, thus being unable to start the combustion.
Meanwhile, although not limited to the CA storage system as referred to above, a certain degree of temperature adjusting width is generally involved if it is intended to maintain the temperature within a refrigerator at a present level. In this case, in a system in which the air-tightness of the refrigerator is very high as in the CA storage system, a large increase or decrease of pressure is produced within the refrigerator by the temperature adjusting width as described above. Therefore, in the CA storage system, a breather bag is employed for absorbing the increase or decrease of pressure in the refrigerator so as to adjust the pressure within the refrigerator, thereby to prevent the outflow of CA gas from the refrigerator or entry of atmosphere into said refrigerator.
However, in the above case, there may arise such a problem that, depending on the position of a circulating blower provided in a circulating path, the interior of the refrigerator is undesirably subjected to a positive pressure or negative pressure, and it becomes difficult to absorb the increase or decrease of pressure due to the temperature adjusting width within the refrigerator by the breather bag, thus resulting in the outflow of the CA gas from the refrigerator or entry of atmosphere thereinto. Particularly, with respect to this problem, in the case where the oxygen concentration within the refrigerator is low, for example, when the oxygen concentration is, at 2% (i.e. 1/10 of the oxygen amount in the atmosphere) the influence of the blowing pressure by the circulating blower is brought into serious question, since the amount of circulating air to be supplied must be 10 times that in the case of the atmosphere.